My invention relates to a coupling capacitor voltage transformer having a tapped secondary winding or separate secondary windings to which burdens may be arbitrarily connected, and particularly to such a transformer having improved phase shift characteristics between the primary winding and the secondary winding.
In high voltage power line systems, it is desirable or necessary that the line voltage and line phase be accurately measured or indicated so that power metering or other functions can be properly provided. Typically, this measurement is made with a plurality of capacitors connected in series between the high voltage line and ground. The primary winding of a coupling capacitor voltage transformer is connected in series with a tuning inductor, and this series circuit is connected between a point in the series of capacitors and ground or a reference point. The transformer is provided with one or more tapped secondary windings which provide isolation and the desired voltage magnitude, usually reduced with respect to the primary voltage. Measuring or switching equipment is connected to a secondary winding. This equipment may be connected across a full secondary winding or across only a portion of a tapped secondary winding, or across several windings, depending upon the characteristics and quantity of such equipment. The coupling capacitor voltage transformers I am aware of had a line to secondary voltage phase relation that depended upon and varied as a function of whether the burden was connected across the full secondary winding or across only a portion of the secondary winding. But since an accurate indication of the line to secondary voltage phase relation is needed to provide the proper measurement, a coupling capacitor voltage transformer having a more accurate line to secondary voltage phase relation is needed.
Accordingly, a primary object of my invention is to provide a new and improved coupling capacitor voltage or potential transformer which has a phase relation characteristic that is substantially constant for a burden connected across the full secondary winding of the transformer, or across only a portion of the secondary winding of the transformer, or across both windings.
Another object of my invention is to provide a new and improved coupling capacitor voltage or potential transformer having a secondary winding with an inductor connected to it so that the effective leakage inductance between the primary winding and this secondary winding is substantially equal to the effective leakage inductance between the primary winding and another secondary winding, thus providing a better primary to secondary voltage phase relation.